$ ~/Projects/build/libasi $ mkdir -p ~/Projects/build/indi-asi
$ ~/Projects/build/libasi $ cmake -DCMAKE_INSTALL_PREFIX=/usr -DCMAKE_BUILD_TYPE=Debug ~/Projects/indi-3rdparty/indi-asi
CMake Error: The source "/home/pi/Projects/indi-3rdparty/indi-asi/CMakeLists.txt" does not match the source "/home/pi/Projects/indi-3rdparty/libasi/CMakeLists.txt" used to generate cache. Re-run cmake with a different source directory.
It seems you are trying to use the build directory you used (successfully...) for libasi to also make indi-asi. Did you neglect to 'cd ~/Projects/build/indi-asi' after you created the directory in the first command, there?